Arteriovenous malformation (AVM) refers to an abnormal connection between arteries and veins. Different types of AVMs occur in different clinical situations, including infantile haemangioma (a benign tumour made up of blood cells), and connections present at birth which are between vessels larger than capillaries (such as veins or arteries) – these are known as high-flow AVM.

The most common form of AVM is low-flow AVM, in which the abnormal connections are in an area with a low blood flow, meaning the space fills and empties slowly. This may be due to compression or gravity, a condition such as Klippel-Trénaunay syndrome or maybe a combination of both these types. Another form of AVM is lymphatic malformations, though these are uncommon and may include cystic lesions (cysts, abscesses or bruising).

Klippel-Trénaunay Syndrome (KTS) is a rare congenital medical condition in which blood vessels and/or lymph vessels fail to form properly. The three main features are a port-wine stain, venous and lymphatic malformations, and soft-tissue enlargement of the affected limb. The condition tends to affect a single limb, usually a leg.

Although AVMs are congenital (present at birth), they are mostly diagnosed in adults under 40, and have a death rate of 10-15%.

In most cases, AVMs have no symptoms and so are discovered by chance, but the symptoms the patient experiences or does not experience depend on the location of the AVM. AVMs sometimes cause intense pain or bleeding and may lead to other serious medical problems. AVMs do not always require treatment.

You may be advised to undergo treatment for the AVM if you experience haemorrhaging, pain, ulceration, if your heart is pumping too much blood, if you have a mass that interferes with normal activity or growth, or if you develop disfiguring lesions.

The only indication that the treatment may not be suitable for you is if your anatomical situation would prevent it, meaning that the structure of the affected blood vessels may prevent treatment from being carried out. It is therefore vital that the interventional radiologist carries out imaging before the procedure to evaluate which type of AVM you have and how the feeding vessels are structured.